1. Field of the Invention
This invention relates to an improved mechanism for forming a liquid-tight seal around the rotary shaft of a liquid pump.
2. Description of the Related Art
A liquid pump has a sealing mechanism for preventing any liquid from leaking out of its casing along its rotary shaft extending through the casing. A known sealing mechanism is disclosed in, for example, Japanese Patent Application Laid-Open No. SHO 55-100421 entitled "Ceramic Sliding Device", or No. HEI 7-19349 entitled "Sliding Device".
The mechanism as disclosed in the former application has one of its rotary and stationary members formed from a sintered product of silicon nitride, while the other is a sintered product of silicon carbide. This mechanism has, however, a drawback which is due to the hardness of the two materials. The two members abrade each other, and the dust produced by their abrasion is caught between the sliding surfaces and accelerates their wear and shortens their life.
The mechanism as disclosed in the latter has a sliding member of carbon and a sliding member of alumina ceramics which has a sliding surface having a roughness Ra of 0.1 to 0.3 micron. It has, however, been found that its sliding member of alumina ceramics fails to provide a good seal.